By means of a new stop-flow technique, which produces migrating waves of materials by reversibly interrupting their transport in nerve axons, we are characterizing the axonal transport of specific substances in adrenergic and cholinergic nerves. We have already studied the transport of dopamine-Beta-hydroxylase and tyrosine hydroxylase in some detail. We proposed to examine the transport of norepinephrine as well, in order to further test the proposed association of the biosynthetic enzymes with the storage sites for this neurotransmitter. We also propose further experiments upon the kinetics of transport to determine the capacity of the transport system and the relationship, if any, between the amount of material transported and the velocity of transport. Experiments will also be carried out to test the proposed role of neuronal microtubules as a mechanism for transport. These experiments will utilize the sharp transitions we have recently noticed in the temperature-dependence of transport, which will be compared closely with biochemical and electronmicroscopic measurements of the behavior of neuronal microtubules under identical circumstances. BIBLIOGRAPHIC REFERENCES: S. Brimijoin and D. Thacker: Effects of 6-hydroxydopamine on axonal transport in adrenergic nerves. In: Chemical Tools in Catecholamine Research. v. I. (Ed. Jonsson, Malmfors, and Sachs), Amer. Elsevier, New York, 1975, pp. 107-113. S. Brimijoin and L. Helland: Rapid retrograde transport of dopamine-Beta-hydroxylase as examined by the stop-flow-technique. Brain Res. 102:217-228, 1976.